When two wireless devices communicate with each other in a wireless network in a traditional manner, each wireless device communicates radio signals with a serving base station of the wireless network by sending uplink radio signals to the base station as well as receiving downlink radio signals from the base station. This is the traditional way of communication in a wireless network also when the two wireless devices are located somewhat close to one another and being served by the same base station. Recently, techniques have been developed to enable such wireless devices in a wireless network to communicate radio signals with each other directly, as controlled by the wireless network and using frequency spectrum licensed to the wireless network, such that each wireless device receives and decodes the actual radio signals that are transmitted directly from the opposite, or “peer”, wireless device. Bluetooth is another example of direct communication between wireless devices, although without control or involvement by any network.
Communication of radio signals may thus take place directly between the two wireless devices without the radio signals being communicated over the wireless network via one or more base stations. In that case, the serving base station allocates radio resources, e.g. defined by time and/or frequency, which the wireless devices are allowed to use in the direct communication. Such direct radio communication between two wireless devices is commonly referred to as “Device-to-Device, D2D, communication” which term will be used throughout this disclosure.
In the field of cellular radio technology, the term “wireless device” is usually used and it will be used in this disclosure to represent any wireless communication entity capable of radio communication with a wireless network including receiving and sending radio signals. Another common term in this field is “User Equipment, UE” which implies that the communication entity can be carried and operated by a human user, examples include mobile telephones, tablets and laptop computers. However, a wireless device in this context is not limited to operation by a human user. It could also be a machine-to-machine type of device operating automatically such as a sensor, counter or measuring entity which may be stationary.
Further, the term “radio access point” refers to a node that can communicate radio signals with wireless devices, which may be a base station belonging to a wireless or cellular network. In the context of such a network, a base station is sometimes also referred to as a radio node, network node, e-NodeB, eNB, NB, base transceiver station, etc. The radio access point discussed in this disclosure may also be another wireless device that in some respect acts in the manner of a base station towards one or more wireless devices. Thus, the term “radio access point” represents any node belonging to a wireless network and which is arranged to communicate radio signals with wireless devices. Throughout this disclosure, the terms “Base Station, BS” and “User Equipment, UE” could be used instead of radio access point and wireless device, respectively. For example, the term “BS” is often used in this disclosure instead of radio access point.
The above D2D communication may thus be employed whenever the two wireless devices, also referred to as “peer devices” or just “peers”, are close enough to one another to be able to receive and decode radio signals transmitted from the opposite peer. Thereby, it may be possible to reduce transmit power in the area and also to reduce interference, as compared to what is required to enable a serving radio access point to communicate radio signals with the wireless devices in the traditional manner.
In a conventional radio communication between a radio access point and a wireless device, a radio signal transmitted by the wireless device may be successfully received and decoded by the radio access point, or vice versa, provided that the current radio conditions allow for sufficient quality of the received signals such that e.g. a received Signal to Interference and Noise Ratio (SINR) exceeds a minimum required threshold or similar. This means that the received signal should not be too weak and/or interfered too much by other radio transmissions in the neighborhood for satisfactory reception and decoding. For example, the wireless device may be situated close to a cell edge and relatively far from the radio access point, or in a spot with bad radio coverage, so that the radio signal fades considerably on its way to the radio access point. Furthermore, the wireless device may in that case need to transmit with increased power in order to provide a sufficiently strong signal at the receiving radio access point, which may cause interference to other nearby communications. Another possibility is to add extra bits which can be used to assist the decoding in the radio access point's receiver although they occupy precious radio resources such that overall data throughput is reduced. In this case it may be more efficient to communicate over a D2D link instead of via the radio access point. It is also possible to take advantage of a combination of cellular and D2D communication, e.g. using network coding (NWC) by the radio access point, where the receiving device can use signals transmitted from both the serving radio access point and the opposite device for decoding.
However, different ways of communication may be more or less favorable to use in different situations depending on the radio conditions and what radio resources are used. Therefore, there is a risk that a way of communication is used that is less efficient and favorable than another way of communication would be. A technical problem discussed in the present disclosure may be defined as a problem of how to select an appropriate way of communication, also referred to as transmission mode, for bidirectional, or two-way, local communications in wireless or cellular networks supporting both D2D and network coding technologies.